[Not Applicable]
1. Field of the Invention
The present invention relates to a golf club having a relatively thin striking plate. More specifically, the present invention relates to a golf club having a thin striking plate with a coating on the exterior surface of the striking plate.
2. Description of the Related Art
Present golf clubs have repositioned weight in order to lower the center of gravity for better performance. This repositioning of weight has for the most part attempted to thin the crown and striking plate of the golf club while precisely placing the weight in the sole of the golf club. However, thinning the striking plate too much may lead to failure of the golf club.
When the striking plate impacts a golf ball during a swing, large impact forces (in excess of 2000 pounds) are produced thereby loading the striking plate. In the relatively thin striking plates of hollow metal woods and cavity-back irons, these forces tend to produce large internal stresses in the striking plate. These internal stresses often cause catastrophic material cracking which leads to failure of the club head.
Computational and experimental studies on hollow metal woods and cavity-backed irons have demonstrated that such catastrophic material cracking most often occurs at impact points on the striking plate. These impact points require added strength to prevent club head failure.
In designing golf club heads, the striking plate must be structurally adequate to withstand large repeated forces such as those associated with impacting a golf ball at high speeds. Such structural adequacy may be achieved by increasing the striking plate stiffness so that the stress levels are below the critical stress levels of the material used in the striking plate. Typically, for metal woods, the striking plates are stiffened by uniformly increasing the thickness of the striking plate and/or by adding one or more ribs to the interior surface of the striking plate.
Uniformly increasing the thickness of the striking plate portion typically requires the addition of large amounts of material to adequately reduce the stress sufficient to prevent impact and/or fatigue cracking. However, the addition of such a large amount of material to a striking plate generally adversely affects the performance of the golf club.
One of the first patents to disclose variable face thickness was U.S. Pat. No. 5,318,300 to Schmidt et al., for a Metal Wood Golf Club With Variable Faceplate Thickness which was filed on Nov. 2, 1992. Schmidt et al discloses thickening the faceplate to prevent cracking.
A further disclosure of variable face thickness is disclosed in U.S. Pat. No. 5,830,084 to Kosmatka for a Contoured Golf Club Face which was filed on Oct. 23, 1996. Kosmatka addresses contouring the face to thicken certain regions while thinning other regions depending on the stress load experienced by such regions. Kosmatka also discloses a method for designing a face plate according to measured stress levels experienced during impact with a golf ball. Kosmatka, U.S. Pat. No. 5,971,868 for a Contoured Back Surface Of Golf Club Face, filed on Nov. 18, 1997, discloses similar contouring for an iron.
A more recent disclosure is Noble et al., U.S. Pat. No. 5,954,596, for a Golf Club Head With Reinforced Front Wall, which was filed on Dec. 4, 1997. Noble et al. discloses a face plate with the thickness portion at the geometric center, and gradually decreasing toward the top and bottom, and the sole and heel. The top and bottom ends along a line through geometric center have the same thickness, and the heel and sole ends along a line through geometric center have the same thickness.
Other references make partial disclosure of varying face thickness. One example is FIG. 8 of U.S. Pat. No. 5,505,453 which illustrates an interior surface of a face with a bulging center and decreasing thickness towards the heel and sole ends, similar to Noble et al. Another example is FIGS. 4C and 4D of U.S. Pat. No. 5,346,216 which discloses a bulging center that decreases in thickness toward the heel and sole ends, and the top and bottom end of the face, similar to Noble et al. However, the prior art has failed to design a striking plate or face plate that is thin and reduces scoreline concentration of the initial shock load during impact with a golf ball.
The present invention is directed at a golf club head having a thin striking plate that has a smooth exterior surface with a thin layer disposed on the exterior surface. The thin layer has a plurality of scorelines to absorb the initial shock load during impact with a golf ball and to distribute and reduce stress loads in the body of the golf club head.
One aspect of the present invention is a golf club head including a body, a striking plate and a thin layer. The body has a crown, a sole, a heel end, a toe end and a hollow interior. The striking plate is attached to the body. The striking plate has an interior surface facing toward the hollow interior and a smooth exterior surface opposite the interior surface. The striking plate has a thickness range of 0.010 inch to 0.200 inch. The thin layer is disposed on the exterior surface of the striking plate. The thin layer has a thickness of 0.005 inch to 0.100 inch, and can have a plurality of scorelines.
Another aspect of the present invention is a wood-type golf club head having a body and a thin layer. The body has a crown, a sole, a ribbon, a striking plate and a hollow interior. The body is composed of a metal material. The striking plate has an interior surface toward the hollow interior and a smooth exterior surface opposite the interior surface. The striking plate has a thickness range of 0.010 inch to 0.200 inch. The body has a volume of 250 cubic centimeters to 400 cubic centimeters. The thin layer is disposed on the exterior surface of the striking plate. The thin layer has a central impact region composed of a polyurethane material having a Shore D hardness greater than 50 for low friction and low energy loss. The thin layer also has a peripheral impact region composed of a polyurethane material having a Shore D hardness lower than 40 for a high friction coefficient and a high energy loss. The thin layer has a thickness of 0.005 inch to 0.100 inch. The thin layer has a plurality of scorelines thereon. The golf club head has a coefficient of restitution of at least 0.83 under USGA test conditions.
Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.